The present invention relates to light detectors and more particularly to a light detector having an ultrafast gated input.
There is a need for a light detector having an input that can be gated on an off over an ultrashort time window, such as in picoseconds. For example, it is well known that Raman scattering signals produced when a sample is excited by a light source respond instantaneously following the shape of the impinging light signal, which may be a pulse on the order of picoseconds, while the fluorescence emission times are generally greater than a few nanoseconds. In order to measure the intensity of the Raman signals it would therefore be desirable to provide a light detector that can be gated on and off for a time period that is not longer than the excitation pulse.
Photomultiplier tubes are well known in the art and commonly used as light detectors to measure the intensity of light impinging thereon.
Streak cameras are about ten years old in the art and have been used, hitherto, to directly measure the time dynamics of luminous events, that is to time resolve a light signal. A typical streak camera includes an entrance slit which is usually rectangular, a streak camera tube, input relay optics for imaging the entrance slit into the streak camera tube, appropriate sweep generating electronics and output relay optics for imaging the streak image formed at the output end of the streak camera tube onto an external focal plane. The image at the external focal plane is then either photographed by a conventional still camera or a television camera. The streak camera tube generally includes a photocathode screen, an accellerating mesh, sweeping electrodes and an phosphor screen. The streak camera tube may also include a microchannel plate. Light incident on the entrance of the streak camera is converted into a streak image which is formed on the phosphor screen, with the intensity of the streak image from the start of the streak to the end of the streak corresponding to the intensity of the light incident thereof during the time window of the streak. In the past, the input optics of the streak camera has been a single lens.
In an article entitled "An Ultrafast Streak Camera System" by N. H. Schiller, Y. Tsuchiya, E. Inuzuka, Y. Suzuki, K. Kinoshita, K. Kamiya, H. Iida and R. Alfano appearing in the June 1980 Edition of Optical Spectra, various known streak camera systems are discussed. The article is incorporated herein by reference.
In U.S. Pat. No. 4,232,333 to T. Hiruma et al there is disclosed a streak image analyzing device in which the output streak image of a streak camera is fed into a television camera. The output of the television camera is fed through a video-mixing circuit to a monitor. The output of the television camera is also fed to an integrating circuit through a gate circuit. The output of the integrating circuit is fed to a memory through an analog to digital converter. The output of the memory is displayed by a display unit and/or fed back into the videomixing circuit.
In an article entitled Picosecond Characteristics Of A Spectrograph Measured By A Streak Camera/Video Readout System by N. H. Schiller and R. R. Alfano appearing in the December 1980 issue of Optical Communications, Volume 35, No. 3. pp. 451-454 a streak camera/video readout system is disclosed. The article is incorporated herein by reference. Another article pertaining to streak cameras and spectrographs is Coupling An Ultraviolet Spectrograph To A SC/OMA For Three Dimensional Picosecond Fluorescent Measurements by C. W. Robinson et al in Multichannel Image Detectors pp. 199-213. ACS Symposium Series 102, American Chemical Society.
Known patents of interest include U.S. Pat. No. 2,823,577 to R. C. Machler; U. S. Pat. No. 3,385,160 to J. B. Dawson et al; U.S. Pat. No. 2,436,104 to A. W. Fisher et al; U. S. Pat. No. 3,765,769 to E. B. Treacy; U. S. Pat. No. 4,060,327 to Jacobowitz et al; U. S. Pat. No. 4,162,851 to A. Wade; U. S. Pat. No. 4,299,488 to W. J. Tomlinson and U. S. Pat. No. 4,320,971 to N. Hashimato et al.
It is the general purpose of this invention to provide a device in which a streak camera is used not for the purpose of time resolving a light signal but rather as a gate for gating the input to a photomultiplier tube over an ultrashort time window.
Accordingly, it is an object of this invention to provide a new and improved light detector.
It is another object of this invention to provide a light detector having an input that can be gated on and off in picoseconds.
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part thereof, and in which is shown by way of illustration, a specific embodiment for practicing the invention. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.